Chemical Reactions and Balancing Equations

In a chemical reaction, starting substances change into new substances. The reactants are what you start with (on the left), and the products are what you make (on the right). An arrow points from reactants to products.

Main Reaction Types

• ●Synthesis: two or more things combine into one. A plus B makes AB.
• ●Decomposition: one thing breaks into smaller pieces. AB makes A plus B.
• ●Single replacement: one element trades places with another in a compound.
• ●Double replacement: two compounds swap partners.
• ●Combustion: a fuel reacts with oxygen, releasing energy as heat and light.

Why You Balance

The law of conservation of mass says matter is not created or destroyed. So you must have the same number of each kind of atom on both sides of the equation. You balance by adding numbers called coefficients in front of formulas. Never change the little subscript numbers inside a formula.

1. 1Count how many of each atom you have on each side.
2. 2Add a coefficient in front of a formula to fix whichever atom is unbalanced.
3. 3Recount and adjust until every atom matches on both sides.
4. 4Check that your coefficients are the smallest whole numbers possible.